The representation of speech and other complex auditory signals in the human brain constitutes a major interdisciplinary challenge for cognitive neuroscience. Understanding in a principled manner how acoustic signals are transformed and ultimately recognized as words in a speaker's mental dictionary requires the integration of knowledge across fields ranging from single-cell recording in auditory cortex to linguistic theory. The research program outlined here is focused on two subroutines in speech processing. In the context of the first specific aim, the hypothesis is investigated that speech is analyzed concurrently on two time scales in human auditory cortex, with one corresponding to analysis at the syllabic scale, another at the segmental (phonemic) scale. This multi-time resolution model, which provides an account of hemispheric asymmetry in audition, is tested in a series of behavioral and electrophysiological studies. The goal is to provide a theoretically motivated and neurobiologically sensible answer to how acoustic signals are fractionated in time and how they map to words stored in the brain. The second aim encompasses both behavioral (often audio-visual) and electrophysiological studies that test how (specifically, how abstractly) speech and words are represented in the human brain. The goal is to test models of the cortical encoding of speech sounds and words. The principal method used in this research program is magnetoencephalography (MEG), typically with parallel behavioral studies performed. Other non-invasive recording modalities are also employed (EEC, fMRI) to validate and extend data from any single approach. ( Successfully perceiving speech and recognizing words are processes at the basis of human communication. A mechanistic characterization of the brain structures that mediate these skills is essential to understand the range of disorders associated with problems in speech processing. Health-related phenomena ranging from dyslexia and autism in childhood to aphasia and Alzheimer's disease in the aging population have been repeatedly linked to problems with the auditory analysis of complex signals and the ability to process words appropriately. The development of innovative diagnostic, interventional, and therapeutic approaches critically depends on our enriched knowledge of the brain basis of the processes underlying human speech.